Surface pumping units for drawing down-hole fluids from wells are well known in the oil field. Such units operate a reciprocating pump which is located down-hole, at or below the fluid level. A counterweighted walking beam arrangement is mounted on a base and driven to move up and down through a limited arc. Flexible wirelines work along the face of an arcuate horsehead at the end of the walking beam to impart a straight, vertical reciprocating stroke to a carrier bar, and in turn to a sucker rod assembly. This assembly includes a round polished rod at the upper end, which enters the well through a well head packing gland. The sucker rod then extends deep into the well to drive a down-hole pump.
The well may be 10,000' deep or more, causing this length of sucker rod to stretch under the load of its weight of over 20,000 pounds. The amount of stretch is not entirely predictable, and a new installation will usually require several attempts to find the proper sucker rod depth adjustment. The sucker rod also tends to stretch under operating loads over long periods, so that a compensating adjustment is needed from time to time. Another consideration is that the required adjustment range increases with well depth.
In some areas there are potential pumping porblems because of down hole gas build-ups. Although it is cumbersome with conventional equipment, many operators periodically adjust the sucker rod depth to bump the bottom of the hole so as to shake any gas bubbles loose.
This is done by stopping the pump near bottom of its stroke and tightening a temporary friction clamp on the polished rod where it will rest on the well head to support the string. The primary clamp, seated atop the carrier bar, is then loosened and respositioned higher on the polished rod. The pump drive is then rotated to bring the carrier bar up against the repositioned clamp, picking up the weight of the sucker rod string and allowing removal of the temporary clamp. Hopefully, the respositioned clamp is properly located and the desired results are achieved without a second try. A reverse procedure is then followed to restore the pump to normal operation. It must be appreciated that working with such massive loads is done carefully, but even so, is always accompanied by the risk of material or personal injury.
There have been efforts to address this task with greater facility, not only for economy of labor cost, but to promote safety with the frequently less experienced help currently available, and to avoid damage to expensive equipment and lost production. Notably Felder, in his U.S Pat. Nos. 4,286,656 and 4,296,678, discloses a hollow hydraulic ram which receives the polished rod for use as a sucker rod jack, and teaches a method of multiple operations for making adjustments greater than the stroke length of the ram.
In actual practice, an adjustment range of 24" or more is useful, and since an inherent need for doing multiple step adjustments would be self defeating, the use of 24" or longer stroke rams is indicated. The collapsed length dimension of a 24" stroke ram is approximately 30", making the extended length about 54". Working clearance at the well center of a typical installation is frequently insufficient for such dimnension, so that there would be interference with either the horsehead above, or the well head below.
The use of such carrier bar devices, prior to the present invention, has also entailed replacement of the carrier bar, and very possibly the connecting wirelines. Since carrier bars are not universally interchangable, with different wireline spacing and connections, a variety of modifications and adaptations have been needed. Also, the hollow piston rams of such prior devices must have at least two seal diameters and, as compared to conventional solid piston rams, are expensive to replace, prone to leakage and difficult to repair.
A first object of the present invention therefore is to provide a sucker rod depth adjusting attachment which avoids interference with pump and well components above and below the carrier beam, and to provide the attachment in configurations suitable to operators and to original equipment pumping unit manufacturers.
A second object of the present invention is to provide a sucker rod depth adjusting attachment which is capable of installation on conventional surface pumping units of various manufacturers and models without replacement or modification of the existing parts.
A third object of the present invention is to provide a sucker rod depth adjusting attachment which minimizes the need for maintenance and furthermore is readily repaired if such need arises.
The present invention accomplishes these objectives in an economical manner, with an attachment that rests atop any conventional, unmodified carrier bar while requiring minimal excess vertical clearance. A cross bar lies transversely across the carrier bar, supporting underslung solid piston rams on each side thereof. The upper piston ends of these rams abut a depth adjusting bar, which matches the general shape of the cross bar and is adjustably positioned above the cross bar by extension or retraction of the rams. Centrally located rod holes in both of the attachment bars align with a similar hole in the carrier bar so that the polished rod can be clamped above the depth adjusting bar as it formerly was above the carrier bar. In this manner, the maximum clearance height requirement is limited to no more than the stroke of the rams, plus the thickness of the attachment bars, or about 30", and this together with the underslung placement of the rams, away from the well center, avoids vertical interference.